1. Field of the Invention
The present invention generally relates to the field of semiconductor fabrication. More particularly, the invention relates to the fabrication of acoustic wave structures in semiconductor dies.
2. Background Art
Bulk acoustic wave (BAW) structures, which can be used in frequency control or filtering applications, can include a piezoelectric layer sandwiched between upper and lower electrodes and an underlying acoustic mirror. When an electric field is applied across the piezoelectric layer via the upper and lower electrodes, electrical energy is converted into acoustic energy in the piezoelectric layer through electromechanical coupling, thereby causing the piezoelectric layer to vibrate and generated acoustic waves. The acoustic mirror, which can include a number of alternating dielectric and metal layers, can be used to trap acoustic energy in the piezoelectric layer by reflecting acoustic energy, thereby preventing acoustic energy loss through transmission into the substrate.
In a conventional BAW structure, such as a BAW resonator, the piezoelectric layer can comprise zinc oxide (ZnO), aluminum nitride (AlN), or other suitable piezoelectric material and the upper and lower electrodes can comprise a high density metal, such as molybdenum (Mo) or tungsten (W), for increased electromechanical coupling. The conventional BAW structure typically utilizes aluminum copper (AlCu) metallization for bond pads and the like, since copper in the aluminum copper reduces undesirable electromigration. However, fabrication of a conventional BAW structure, such as a BAW resonator, requires one process chamber for forming the piezoelectric layer and another process chamber for forming the aluminum copper metallization used in the BAW resonator, which can undesirably reduce manufacturing efficiency and increase manufacturing cost.